The invention relates to a starting block for swimming competitions. This type of device is intended to determine the moment when the swimmer takes his departure and more precisely detect false starts or relaying failures.
Known starting blocks such as represented in FIG. 1 are formed of a platform 1 pivotally mounted as shown at 2 on a fixed base 3. Platform 1 may pivot about the articulation 2 under the effect of a force P representative of the weight of the swimmer and against the force of a spring 4 and may close electric contacts 5 the closure of which will indicate the presence of the swimmer on platform 1. As soon as the swimmer leaves the platform, spring 4 urges the platform against a stop 6 and contacts 5 open thereby signalling the departure of the swimmer.
According to current usage such as starting blocks are used only to detect relaying faults. When a swimmer who must be relayed completes his course through touching the touch pad indicating the end of his course the electronic measuring equipment indicates that the relaying swimmer continues to be on platform 1 so long as contacts 5 remain closed.
Although currently utilized, this type of starting block presents various and serious draw-backs.
The price of manufacture is very high in view of the fact that the pivot must be of an extremely resistant and very careful construction in order to be of long life and to maintain its qualities during numerous transports to and assemblies in different swimming pools.
A good electric contact switch is quite difficult to obtain, since it must not open and close merely under the effect of vibrations of the platform and must thus show a preliminary displacement and relatively large closing displacement. Such displacement of the platform is annoying for the swimmer if it should exceed 2-3 mm. The adjustment of this contact moreover is quite delicate and it is necessary to readjust it following each transportation or disassembly of the starting block.
The platform which must be very resistant is from this factor quite heavy and to overcome its inertia the return force of the spring must be quite considerable on the order of several decanewtons. Just prior to the departure of the swimmer there is produced a lightening phenomenon: the swimmer lightens the platform in order to gather himself together so as better to relax and to realize a good departure. During this phase the vertical component of the force exerted by the swimmer on the platform descends to a minimum which may be in the order of 2-3 decanewtons and is annulled at the instance of departure only a fraction of a second later (on the order of 1 tenth), after having passed once again to a maximum. The contacts may thus open and close before the effective departure of the swimmer, this phenomenon causing an uncertainty or error. On the other hand should the spring be weaker such undesired opening may be avoided, but in this case the considerable inertia of the platform and friction within the bearings may falsify the result, the swimmer having left the starting post well before the spring has been able to return the platform.
Such movement of the platform as well as slapping of the platform on its stop is moreover annoying for the swimmer.